Apple rootstock named `Geneva 11`

ABSTRACT

A new and unique apple rootstock, `Geneva 11` that is dwarfing and resistant to crown rot and fire blight.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/760,293,filed Dec. 4, 1996, now abandoned, which is a continuation ofapplication Ser. No. 08/609,417, filed Mar. 1, 1996, now abandoned,which is a continuation of application Ser. No. 08/353,305, filed Dec.5, 1994, now abandoned, which is a continuation of application Ser. No.08/184,627, filed Jan. 21, 1994, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a new and distinct asexually-reproducedcultivar of apple tree, `Geneva 11`, which we discovered in a testplanting belonging to New York State Agricultural Experiment Station,Cornell University, Geneva, Ontario County, N.Y. This discovery is aproduct of the apple rootstock breeding program of the New York StateAgricultural Experiment Station ("Station").

ORIGIN

In March 1978, pollen was collected from a Malus×robusta cv. Robusta 5apple tree and used to pollinate emasculated flowers of aMalus×domestica cv. Malling 26 (M.26) apple tree growing in Stationgreenhouse No. 13. The seeds were harvested from fruit produced fromthis cross and were stratified in November 1978. After stratification,180 germinating seeds were planted in a Station greenhouse in January1979. When the emerging seedlings were about 2.5 cm tall, we inoculatedwith 15 isolates of the fungi Phytophthora cactorum and Phytophthoramegasperma, which are causal agents of certain crown and root rots. Theflat was flooded to mid-hypocotyl level of the seedlings, and kept atabout 23° C. for 7 days; 104 seedlings survived this treatment. Thesurviving seedlings, when 10 to 15 cm tall, were inoculated in theirshoot tips with about 10⁶ cells of isolate Ea 273 of the bacteriumErwinia amylovora, the causal agent of the fire blight disease, using a26-gauge hypodermic syringe. Four subsequent inoculations with E.amylovora isolate Ea 273 were made in summer and autumn, 1979. Theseedling designated 7826R5-011, later tested as CG.11 and now named`Geneva 11`, was very resistant; lesions were less than 2 cm long.Later, lesions 5 cm long developed when Geneva 11 shoots were inoculatedwith E4001A, a very virulent strain of the bacteria. The survivors wereinoculated repeatedly with woolly apple aphids (Eriosoma lanigerum);very susceptible individuals were discarded. The plant now designated`Geneva 11` was moderately susceptible to woolly aphids. Seedlings withvery small leaves and those displaying either root initials or spineswere also discarded.

We selected 15 Erwinia amylovora-resistant seedlings and planted them astrench layers on the Station's Loomis Farm in April 1980. Rooted linerswere harvested in late fall 1983 and were planted in the Station nurseryin the spring of 1984. Maiden trees of the cultivars `Topred Delicious`,`Summerland McIntosh` and `Mutsu` were produced by budding the `Geneva11` liners. These trees were subsequently planted in trial orchards atthe Station at the United Stated Department of Agriculture AppalachianFruit Research Station, Kearneysville, W. Va., Hilltop Orchards,Hartford, Mich.; Littletree Orchards, Newfield, N.Y.; and Brown Orchards(Indian Creek Fruit Farm), Ithaca, N.Y.

In these test plantings, trees on `Geneva 11` were similar in size tothose on `Malling 26` rootstock, based on comparison with the checktrees in the same test plantings. Trees on `Geneva 11` began floweringearly, usually the 2nd or 3rd year in the orchard; this was especiallynoteworthy for `Mutsu` cultivar, which in New York normally beginsfruiting in the 3rd or 4th year when grafted on the precocity-inducingrootstock `Malling 26`. All of the cultivars that have been tested on`Geneva 11` have demonstrated high production efficiency, equal to ormore than that experienced with the efficient `Malling 26` rootstock.

COMPATIBILITY

We have observed no symptoms of incompatibility with 16 trees of the 3fruiting cultivars mentioned above. Besides these, we have grafted`Jonagold`, `Melrose`, `Empire`, `Gala`, and `Liberty` cultivars `Geneva11`; in the nursery we have observed no symptoms of incompatibility. Allscionwood used was free from known harmful viruses.

PROPAGATION

We have propagated `Geneva 11` asexually by budding and grafting ontoseedling and clonal rootstocks; by root cuttings; by hardwood cuttings;by greenwood cuttings; and by conventional layering. These asexualpropagules have remained true-to-type with these methods of asexualpropagation. We have also propagated `Geneva 11` readily in tissueculture; however, `Geneva 11` appears to be especially sensitive toepigenetic changes, apparently induced by the growth regulatorenvironment in the tissue culture medium: leaf width is significantlyreduced; more and longer spines are produced in the stoolbed; shootsmature very late; susceptibilities to fire blight and to powdery mildeware increased; and rooting in the stoolbed is accelerated. In thestoolbed, these changes disappear with time. The effects described hereoccurred with a particular set of tissue culture events. Other tissueculture regimens, with different hormonal concentrations, differentnumbers of transfers and different microenvironments, have yieldeddifferent results. In general, these epigenic effects are maximized withhigher concentrations of growth regulating substances in the media,and/or with prolonged culture, and/or numbers of transfers. We have noevidence they are related to juvenility. We do not consider them to beontogenic effects. The experience thus far suggests these epigeniceffects are temporary.

We have also used `Geneva 11` as a pollen parent in our breedingprogram. `Geneva 11` is considered to be highly heterozygous because itsparents are very different from each other. Its seedlings are muchdifferent from both parents and from each other. No progeny testing hasbeen carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph showing the topside of a `Geneva 11` leaf and theunderside of a `Geneva 11` leaf.

FIG. 2 is a photograph of leaves of dormant `Geneva 11` shoots that havebeen etiolated in sawdust mulch through the previous growing season.

FIGS. 3 and 4 show that pubescence on dormant shoots is light. Lenticelsare very slightly raised, round or nearly so, greyed orange in color.Dormant buds are obtuse, sessile, brown; a pronounced ridge is typicallyobserved centrifugal to the median bud trace and extending about 1 mmbelow bud insertion.

FIGS. 5 and 6 show that shoots in the layer bed are straight and 40% areclean-shanked. Several short spines occur on about half the shoots.Shoot maturation and leaf fall are moderately early.

FIG. 7 shows that in the layer bed, `Geneva 11` shoots root from the budgap. Relatively few roots are produced; these tend to be moderatelycoarse, with few branches.

FIG. 8 shows that leaves on shoots derived from tissue culture aremoderately susceptible to powdery mildew, although infection on theshoot is rare. We have not seen powdery mildew on leaves of shootsderived from normal layer bed propagation.

DESCRIPTION OF THE INVENTION

Following is a detailed description of our new cultivar, `Geneva 11`.Accompanying FIGS. 1-8 depict behavior in the stoolbed and leaf andshoot characteristics. The numerical color specifications employed arethose of The Royal Horticultural Society Colour Chart (1976). Botanicaldescriptions follow Manual of Cultivated Plants (Bailey, 1949).

TREE HABIT

The unbudded tree of `Geneva 11` is a small shrub, typically standingabout 2.5 m tall×about 2 m wide. There is no single dominant trunk, butrather 4 to 8 shoots arising from the roots (FIG. 5). The unbudded treeis a dwarf, comparable to a `Malling 26` apple tree of similar age.Growth rate is moderately slow, with early cessation of growth typicallyoccurring about 1 week earlier than for `Malling 26`. Spring budbreak ismidseason to moderately late. Over a two to four year period, anunbudded tree may produce two to five suckers, which become multiplestocks; in contrast, the unbudded tree of `Malling 9` produces amoderate number of suckers and there are many shoots developing intosmall stocks. As an unbudded plant, `Geneva 11` is not precocious; wehave not observed flowers and we have not observed fruit until December1998. We do not know whether `Geneva 11` is a self-fertile.

DORMANT SHOOTS

In the stoolbed and nursery row, dormant matured shoots of currentseason (one-year shoots) are Brown 200B where exposed to full sunlight,grading to grey-brown 199A and 199B with diminished light exposure(FIGS. 5 and 8). Pubescence is light (FIGS. 3 and 4). Shoots are ofbelow average vigor, usually about 50 to 70 cm in the stoolbed. Midshootinternodes are below average, ranging from 14 to 17 mm. Profuse rootprimordia develop on etiolated shoot base of `Geneva 11` and erupt bothfrom supranodal tissue and from internodal sites (FIG. 2). Axillary budsare obtuse, sessile, usually somewhat appressed. Usually the barksurface immediately below the centrifugal to the median leaf traceexhibits a sharp 1 mm extension. The bark on one-year shoots and ontwo-year shoots is the same and is epidermal and therefore is not barkin the botanical meaning. Axillary buds are vegetative only. Bud scalesare average size, brown 200A, with heavy greyed-white 156D pubescence atthe bud tip. Lenticels are round, small in size, mostly 0.2 to 0.3 mmdiameter, very slightly raised, greyed-orange 165C in midshoot section(FIGS. 3 and 4). Burrknots are not present on 1- or 2-year old shoots; aroot initial occurs on about 10% of older shoots, always from thebud-gap, usually just above the basal bud scale scars. When shoots of`Geneva 11` have been etiolated, root primordia develop both from thesupranodal bud-gap tissue and randomly in internodal sites. Nosphaeroblasts have been observed. Spring budbreak is early midseason,several days before `Malling 26`. Autumn leaffall is moderately early,usually a week to ten days before M.26. Wood is not brittle, similar toM.26. In the stoolbed, 40% of the shoots have no spines and anadditional 25% have only 1 or two; the remaining shoots averaged 6spines per shoot; spines averaged 32 mm long. One-year-old shootsharvested from layer bed exhibit typical 2/5 phyllotaxy, and spines arepresent on about half of said shoots, and stipules are reduced orabsent.

LEAVES

Leaves are simple; ovate and about one and one-half times long as broad(FIGS. 1 & 8); lamella somewhat wavy; tip acuminate; margin acutelyserrate, usually doubly, sometimes triply; about 4 serrations per cm;base obtuse, usually slightly asymmetrical; stipules small, usuallyabout 1×10mm. Lamellae average 75×48mm. Adaxial lemella surface green137B; abaxial surface yellow-green 147B; upper surface nearly glabrous;short pubescence on lower surface. Petiole 20 to 25 mm long. Leaf poisetypically 35° to 45° from shoot. The coloration of the veins andpetioles varies with culture and climate.

FRUIT

Flowers and fruit are not normally observed on this rootstock cultivar,since all shoots are normally harvested after one season's growth.However, in an abandoned test plot in Geneva, N.Y., one two-year suckerof `Geneva 11` was discovered bearing apples. On this plant, fruits wereborne on very short spurs formed the previous year. Fruits of `Geneva11` are oblong-conic, 30 to 40 mm long×22 to 32 mm diameter. Skin isyellow-orange 19C with overcolor orange 24A on side exposed to sun.Peduncle is long, 22 to 30 mm, very flexible and thin, less than 1 mmdiameter, non-brittle. Calyx is protuberant and closed. Flesh isfine-graned orange-white 159B. Calyx tube is closed and basin very deep.Seeds are dark brown greyed-orange 166A, 5 to 7 mm long×3 to 4 mm.

ELECTROPHORESIS

Horizontal starch gel electrophoresis was conducted on extracts fromdormant lateral buds of `Geneva 11`. The isozymes glucosephosphateisomerase (GPI), phosphoglucomutase (PGM) and 6-phosphogulconatedehydrogenase (6PGD) were used to obtain comparisons between `Geneva 11`and its near-relative, `Malling 9`. `Malling 9` is the mother of`Malling 26` which is the mother of `Geneva 11`. `Malling 9` is areference clone, used worldwide in chemical identification of applerootstocks. The GPI and PGM systems are especially useful indistinguishing among apple rootstocks derived from `Malling 9`. Theelectrophoresis showed the following differences between `Geneva 11` and`Malling 9`: The 6PGD system differentiated the two rootstocks in that`Geneva 11` exhibits a faint but distinct band near the anode, which isabsent in the case of `Malling 9`. The GPI system differentiated the tworootstocks at three, possibly four loci in that for `Geneva 11` there isa band closer to the anode than in the case of `Malling 9` and thebanding pattern between the bands closest to the anode and closest tothe cathode is different for `Geneva 11` compared to that for `Malling9`. The two clones were similar only on the bands nearest the cathode;this band appears to be similar on a very large number of Maluscultivars. In the PGM system, `Geneva 11` exhibits a banding near thecathode just downstream from the band nearest the cathode that is absentfor `Malling 9`. The data shows that `Geneva 11` may be distinguishedfrom `Malling 9` by at least five banding patterns exhibited on theisozyme systems 6-PGD, GPI, and PGM. The method of distinguishing applerootstocks by isozyme banding patterns is described in Samimy, C. andCummins, J. N., Hort. Science 27(7), 829-831 (1992).

USEFULNESS

`Geneva 11` is a dwarfing apple rootstock that will directly challengethe `Malling 26` rootstock, which is susceptible to crown and root rotsand very susceptible to fire blight. `Geneva 11` survived inoculationwith two of the most important incitants of crown and root rots; it maytherefore have tolerance to certain crown and root rots caused byspecies of the Phytophthora fungus. The fire blight disease is limitingto apple production in many parts of the United States, includingCalifornia, Washington, the Mid-South and the eastern seaboard states,especially when dwarfing rootstocks in the `Malling 26` class aredesired. `Geneva 11` is moderately resistant to fire blight, and Geneva11 will be especially valuable in those areas in which fire blight isendemic. `Geneva 11` is moderately resistant to powdery mildew(Podosphaera leucotrichum) in the layerbed and nursery. We have notobserved apple scab (Venturia inaequalis) on `Geneva 11` but nodefinitive testing has been carried out. Both these diseases are ofminor importance in the nursery, and foliage diseases do not appear onthe rootstock in the orchard. In the orchard, anchorage of grafted treesis similar to that of trees on `Malling 26`, but because of theprecocity induced by `Geneva 11`, permanent support is stronglysuggested. In the budded tree in the orchard, very few suckers areproduced and they are not exuberant. `Geneva 11` will be used as arootstock in high density plantings, mostly at densities of about 1,000trees per hectare. We do not expect that either conventional trellissupport or espalier training will be applied; trees on `Geneva 11` donot require the level of support offered by conventional trellis, andthey are usually too vigorous for espalier training. We expect that`Geneva 11` will be extensively used in vertical axis systems and willsometimes be trained to unsupported central leaders. `Geneva 11` has nopotential as an ornamental crabapple.

What is claimed is:
 1. A new and distinct cultivar of apple tree,substantially as shown and described herein, characterized particularlyas to novelty by being a dwarfing rootstock that is resistant to fireblight.